Wow that's a big pond!
Well some ideas, if you slope some of it gently into the rest of the garden with soil over pond liner you can create a bog area and grow marginals. Plants like Gunnera mantica love that sort of thing and produce leaves up to 6 feet across which would fit in well with such a large pond.
http://www.splashgordon.co.uk/gallery/index.ht m
If the ponds having such work done you could think about a jetty a bit like this:
http://www.worldofwater.com/news/news_item.asp ?NewsID=32 maybe extending from the patio or decking
Or even a hut in the middle with a drawbridge you could pull up and go and hide yourself away in?
Waterfalls are a favorite, you might have to add some height if it's very flat but it sounds as if you're pumping a lot of water anyway so diverting some of it to add some motion might help.
some other pictures here:
http://www.splashgordon.co.uk/gallery/index.ht m